Gated photocathode arrays as sources for multibeam electron nanolithography

Abstract

Multiple electron beams will need to expose large areas of resist in parallel rapidly if maskless electron lithography of high-density nanoscale structures is to become a production tool. This will require large arrays of gated submicron scale sources for multiple beams with gate changeable currents. In this research and development a small 3×3 array was fabricated using a computer controlled focused ion beam milling machine (FIB). This gated array electron source was tested first in a vacuum chamber without optics to test the operation of the gates in preparation for installation in a column with electrostatic lenses, stigmation, steering, scanning and secondary electron imaging. A primary goal for the project is the exposure of nanoscale lines in resist. The fabrication of a 3×3 test array used a combination of sputter deposition, FIB microforming and micromachining of the necessary metals and insulators. The photoemitting film for each of the gated sources was a FIB deposited 15 nm thick layer of Pt. The initial tests on these gated photocathodes are encouraging, by changing the gate voltage we can change the photoemission current. In addition to the work on the fabrication of the gated arrays, blanket thin film materials are being tested for stability and photoyield for possible use in the gated arrays. In this work a range of thicknesses of glow discharge carbon was deposited on the Ti coated substrates. The 20 nm thick carbon film produced the best performance, a stable 7nA∕mW photoyield. Carbon photocathodes 15 nm, 30 nm, and 60 nm thicknesses were stable but lower at 3.7, 3.6, and 1.3nA∕mW, respectively. A new experimental chamber is currently under construction to allow us to investigate the feasibility of using our gated photocathode arrays to expose PMMA or other suitable electron sensitive resist materials. The photoelectron column is made from a modified FEI 600 series FIB column.